Wide open space in empty amphitheatre (5)
I believe the answer is:
agape
'wide open' is the definition.
(I've seen this before)
'space in empty amphitheatre' is the wordplay.
'space' becomes 'gap' (gap is a kind of space).
'in' means one lot of letters goes inside another.
'empty' suggests removing the centre.
'amphitheatre' with its centre taken out is 'ae'.
'gap' put within 'ae' is 'AGAPE'.
(Other definitions for agape that I've seen before include "love a Christian shows" , "religious feast" , "showing disbelief" , "(Of mouth) wide open" , "love feast" .)